He was not charged with Mr Nguyen's murder until 2016 after a cold case review by police.

At his judge-alone trial in the Supreme Court, Marotta admitted stabbing Mr Nguyen but pleaded not guilty, maintaining he was not criminally responsible for the crime because he was not of sound mind at the time.

Murder weapon also used in nightclub stabbing

The court was told Marotta suffered from paranoid schizophrenia and was hearing voices from God that were telling him to kill people.

The court also heard the knife he used to stab Mr Nguyen was the same weapon he had used to stab two people in a Fremantle nightclub in 1988.

He was jailed for that crime and the weapon was returned to him when he was released from Fremantle prison.

The murder trial was told police had statements from people who were in jail with Marotta in Queensland, who said Marotta had boasted about "getting away with murder" in Perth and claimed he had "outsmarted' the WA Police.

WA Police did receive information in 1990 that Marotta could be a person of interest in Mr Nguyen's murder, but the court heard after interviewing him they formed the view "there was no direct evidence linking him to the crime" and he was released.

Just over four weeks later, he committed the Queensland stabbings.

Supreme Court Justice Lindy Jenkins imposed a custody order on Marotta under the Metal Health Act, under which he can be indefinitely detained at a secure psychiatric facility for treatment.